How to Bake a Displacement / Height Map from a High Poly to a Low Poly Mesh?
You should be able to use Blender 2.79b for baking the displacement until it is available in 2.8x

https://download.blender.org/release/Blender2.79/

Thanks for sending the .blend - it seems that your model was too small



So, when I scaled it to be roughly dimensions x=15, y=12 and z=8 and then applied the scales for both objects CTRL+A, the baking was successful with the values Distance: 0 and Bias: 0

And, you get even greater results if you scale it then with 10 and apply the scales.